Distributing petrofacies using analytical modeling. At least some of the illustrative embodiments are methods including: creating, by a computer system, a geocellular model of an underground formation, the creating by: reading a first value of a first rock property associated with a first well log; associating the first value of the first rock property with a first cell of a plurality of cell of the geocellular model; assigning a value of the first rock property to each cell of the plurality of cells based on the first value and a datum of information, the datum of information distinct from the first value.